The present invention relates to a method for estimating the end-of-stroke positions of moving members of electromagnetic actuators for the actuation of intake and exhaust valves in internal combustion engines.
As is known, drive units are currently being tested in which the actuation of the intake and exhaust valves is managed by using actuators of electromagnetic type, which replace purely mechanical distribution systems (camshafts).
These actuators in particular comprise a pair of electromagnets disposed on opposite sides of a moving ferromagnetic member connected to a respective intake or exhaust valve and held in a rest position by elastic members (for instance a spring and/or a torsion bar). The moving ferromagnetic member is actuated by applying a force generated by the electromagnets in order to be brought into contact alternatively with one or other of these electromagnets, so as to move the corresponding valve between a closed position and a position of maximum opening according to desired timings and trajectories. In this way, it is possible to actuate the valves according to optimum lift profiles in any operating condition of the engine, thereby substantially improving overall performance.
Obtaining an actual increase in the efficiency of the engine is conditioned, however, by the precision of the systems and methods used for the control of the actuators. In order, in particular, accurately to control the force transmitted by the electromagnets to the moving member and thus the movement of the valve, it is indispensable to have an accurate measurement of the distances intervening between the moving member and the polar heads of one or the other electromagnet. As shown by way of example in FIG. 1, the force F that an electromagnet is able to transmit to the moving member depends, the current absorption being equal, in a highly non-linear manner on the distance D between the polar head of the electromagnet and the moving member. An error, even of a few microns, in the measurement of the distance D, in particular for low values of the latter, may therefore compromise the efficiency of the control and thus entail a substantial deterioration of the performance of the engine.
This is a serious drawback, given that internal combustion engines are subject, during their use, to substantial temperature variations which cause expansions and/or contractions of the materials, especially of the metal parts. Consequently, even the polar heads of the electromagnets may expand or contract as a function of temperature, thereby affecting the measurement of the distances between these electromagnets and the moving member.
The object of the present invention is to provide a method for estimating the end-of-stroke positions of the moving member which makes it possible to remedy the above-mentioned drawbacks and, in particular, makes it possible to reduce the overall consumption of electrical power.
The present invention therefore relates to a method for estimating the end-of-stroke positions of moving members of electromagnetic actuators for the actuation of intake and exhaust valves in internal combustion engines, in which an actuator is coupled to a respective intake or exhaust valve and comprises a moving member actuated magnetically in order to control the movement of the valve, a sensor supplying a position signal representative of a current position of this moving member and a first and a second electromagnet disposed on opposite sides of this moving member, wherein this moving member can move between a first end-of-stroke position in which it is disposed in contact with the first electromagnet and a second end-of-stroke position in which it is disposed in contact with the second electromagnet, which method is characterised in that it comprises the stages of:
a) checking whether the moving member is in a condition of stationary contact; and
b) determining a magnitude correlated with this current position, if the condition of stationary contact is verified.